U.S. Pat. No. 3,996,626 schematically shows how a typical intraocular lens is surgically implanted within the eye. An optical section fits against one face of the iris (often the anterior) and two or more retention loops fit against an opposite face of the iris (often the posterior). Each iris retention loop has a pair of shank sections which are secured to the optical section to provide a space for receiving the iris. It is important to firmly lock the shank sections to the optical section to prevent any change in the length of the shank section.
The above patent describes a process wherein the shank sections are positioned in passages of the optical section so that a portion of the shank sections protrude beyond a forward surface of the optical sections. Enlarged bulbular portions are formed on such protrusions. The bulbular portions are then driven into the passages of the optical section with a vibrating punch to cause the lens to distort outwardly within a central portion of the passage to "cold flow" and form a pocket for the bulbular portion. Such "cold flow" could stress the optical section and change its optical properties.
Another approach to maintaining a precise length of the shank sections for receiving the iris is described in U.S. Pat. No. 3,991,426. Here a series of small individual screws are secured to the optical section and pointed heads of the screw pierce the iris. A separate snap-on ring fits over the protruding heads of the screws to act as a retainer and thereby replace the conventional iris loops that are integral with their shank sections. In addition to requiring complicated special tools for use during the steps of piercing the iris and assembling the snap ring, the individual screws could possibly twist within the snap ring to loosen and increase the space in which the iris fits.
Retention loops of a special material, such as Supramid (a Nylon type material), have been heated and forced into a conical recess in the optical section in U.S. Pat. No. 3,994,026. The optical section of an intraocular lens is usually made of polymethylmethacrylate (PMMA). The machined conical recess of this patent would have some surface roughness formed during the machining step which would have a slight clinging effect on the Supramid shank section. In practice, such design has limited holding power and the shank section could be pulled out of this conical recess with a small force. Because of the dissimilarity of materials, there is little, if any, fusion bond between the shank section and the optical section, particularly since the optical section is not heated to its softening point. Such high temperature heating would alter the optical properties of previously ground or molded and polished optical sections.